Uropathogenic Escherichia coli Induces Extrinsic and Intrinsic Cascades To Initiate Urothelial Apoptosis

Abstract

A murine model of urinary tract infection identified urothelial apoptosis as a key event in the pathogenesis mediated by uropathogenic Escherichia coli (UPEC), yet the mechanism of this important host response is not well characterized. We employed a culture model of UPEC-urothelium interactions to examine the biochemical events associated with urothelial apoptosis induced by the UPEC strain NU14. NU14 induced DNA cleavage within 5 h that was inhibited by the broad caspase inhibitor ZVAD, and urothelial caspase 3 activity was induced within 3 h of exposure to type 1 piliated NU14 and was dependent upon interactions mediated by the type 1 pilus adhesin FimH. Flow cytometry experiments using chloromethyl-X-rosamine and Indo-1 revealed FimH-dependent mitochondrial membrane depolarization and elevated [Ca 2؉ ] in , respectively, indicating activation of the intrinsic apoptotic pathway. Consistent with this possibility, overexpression of Bcl XL inhibited NU14 activation of caspase 3. Immunoblotting, caspase inhibitors, and caspase activity assays implicated both caspase 2 and caspase 8 in apoptosis, suggesting the involvement of the intrinsic and extrinsic apoptotic cascades. To reconcile the apparent activation of both extrinsic and intrinsic pathways, we examined Bid-green fluorescent protein localization and observed translocation from the cytosol to mitochondria in response to either NU14 or purified FimH. These data suggest that FimH acts as a tethered toxin of UPEC that activates caspase-dependent urothelial apoptosis via direct induction of the extrinsic pathway and that the intrinsic pathway is activated indirectly as a result of coupling by caspase 8-mediated Bid cleavage.

Inactivation of Host Akt/Protein Kinase B Signaling by Bacterial Pore-forming Toxins

“…For example, the HlyA-positive UPEC isolate CP9 was recently shown to induce rapid activation of proapoptotic executioner caspases in neutrophils much more efficiently than a HlyA-negative mutant (Russo et al, 2005). Relative to an isogenic hlyA mutant, the wild-type CP9 strain also induces more robust exfoliation of bladder epithelial cells (Smith et al, 2006), a phenomenon that seems to involve activation of apoptotic pathways (Mulvey et al, 1998;Schaeffer et al, 2004;Klumpp et al, 2006).…”

“…Recently, it has been suggested that the FimH adhesin localized at the tips of type 1 pili can function as a tethered toxin (Klumpp et al, 2006), raising the possibility that FimH functions synergistically with HlyA in promoting Akt dephosphorylation. However, we found that a UTI89 ⌬fimH mutant is able to inactivate Akt like the wild-type isolate, indicating that HlyA-mediated dephosphorylation of Akt does not require functional type 1 pili ( Figure 2E).…”

“…During the course of an infection, UPEC can stimulate a number of antimicrobial, proinflammatory, prodifferentiation, proliferation, and host cell death pathways (Mulvey, 2002;Mysorekar et al, 2002). In some cases, UPEC can reportedly modulate these signaling events, causing attenuation of host inflammatory responses and potentiating host apoptotic cascades (Klumpp et al, 2001(Klumpp et al, , 2006Hunstad et al, 2005;Billips et al, 2007). These phenomena have been linked in part to the suppression of nuclear factor-B (NF B) activation and downstream signaling by unknown factors associated with UPEC (Klumpp et al, 2001;Hunstad et al, 2005).…”

“…In contrast, infection with WAM783, which carries the ␣-hemolysin operon lacking hlyC, had no inhibitory effect on Akt activation. These results indicate that pore formation by HlyA, after HlyA insertion into host membranes, is required to stimulate Akt dephosphorylation.Recently, it has been suggested that the FimH adhesin localized at the tips of type 1 pili can function as a tethered toxin (Klumpp et al, 2006), raising the possibility that FimH functions synergistically with HlyA in promoting Akt dephosphorylation. However, we found that a UTI89 ⌬fimH mutant is able to inactivate Akt like the wild-type isolate, indicating that HlyA-mediated dephosphorylation of Akt does not require functional type 1 pili ( Figure 2E).…”

Inhibition of EGFR pathway signaling and the metastatic potential of breast cancer cells by PA-MSHA mediated by type 1 fimbriae via a mannose-dependent manner

“…Lectin-like type 1 fimbriae are also responsible for the mannose-sensitive (binding) adhesion to host (mammalian) cells (Schilling et al, 2001;Duncan et al, 2005). Such microbe-host protein-carbohydrate interaction (Karlsson, 2001) is not only the essential step to produce infection, but also it leads to a status alternation of the host cells, for instance, the induction of apoptosis (Mulvey et al, 1998;Klumpp et al, 2006). Engineered bacteria are able to help control cancer (Jain and Forbes, 2001).…”